1. Technical Field
The invention disclosed broadly relates to data processing technology and more particularly relates to input devices for use in conjunction with visual displays.
2. Background Art
In data processing systems, a central processor executes a sequence of stored program instructions to process data provided by an input device and to present the results of the data processing operations to an output device. Data processing results can be presented in either alphanumeric text or in graphical form and a universal mechanism for manifesting those results is by means of a visual display device such as a cathode ray tube monitor, a gas panel display, an array of light emitting diodes, or other types of visual display devices. Frequently, the results presented to the user on a visual display device, will require the user to provide additional data to the data processing system. Various types of data input devices have been employed in data processing systems, for example keyboard input, graphical tablet input, and various forms of display surface inputs. Human factors studies have shown that by providing a means for inputting data on the visual display screen itself, the user can achieve the most closely coupled interactive operations with the data processing system. When the user responds to visual signals output at the face of the visual display device, by inputting signals at that same visual display surface, an accuracy and immediacy in the interaction between man and machine can be achieved. This form of input device is easy to learn to use and seems the most natural and user-friendly to the operator
Various types of interactive input devices for use at the display surface have been provided in the prior art. One of the first forms of interactive devices was the light pen, which is an optical detector provided in a hand-held pen, which is placed against the display surface of a cathode ray tube screen. When the dot of light represented by the scanning raster is detected by the light pen, the coordinates of the raster dot are attributed as the location of the hand-held pen. Another type of interactive input device for use on a display surface is the mechanical deformation membrane, which is a transparent laminate placed over the display surface. The laminate consists of two conductor planes respectively deposited on a flexible medium so that when the user mechanically displaces one of the conductor planes by a finger touch, the conductors are brought into electrical contact with the conductors in the second plane. The electrical resistance of the conductor plane is changed as a function of the position of the finger touch on the membrane and appropriate electronics are provided to translate that resistance value into the position attributed to the finger touch.
Opaque graphics tablets, upon which a sheet of drawing paper can be supported for tracing with an electronic stylus, have been provided in the prior art. In opaque graphics tablets, a horizontal wire grid and a vertical wire grid are embedded in the surface of the tablet. The wires in the tablet are driven with a signal which is electromagnetically radiated from the surface of the tablet and which is received by a pickup stylus connected to a signal detector. In one type of opaque graphics tablet, a field gradient is imposed from one side to the other side of the tablet and the strength of the field as picked up by the stylus, is correlated with the position attributed to the stylus. Another approach has been described by H. Dym, et al. in U.S. Pat. Nos. 3,992,579; 3,999,012; and 4,009,338, those patents being assigned to the IBM Corporation. Dym, et al. describe driving the conductors embedded in the opaque graphics tablets so that they are selectively energized with 40 kilohertz signals in a multiple stage operation to first determine the stylus proximity to the surface of the tablet and then to track the position of the stylus along the surface of the tablet in the horizontal and vertical directions. During the proximity stage of operation, the conductors in all regions of the tablet surface emit signals which are detected by the stylus as it approaches the surface. When the amplitude of the received signals is great enough, the operation then changes into the locate and tracking mode which is programmed to produce periodic indications of the stylus position with respect to the horizontal and vertical conductors embedded in the tablet.
The popularity of the Personal Computer can be attributed, in part, to the enhanced productivity which can be achieved by applying data processing techniques to the execution of tasks which were previously done manually. Typical applications employing an interactive input at the display surface of the monitor in a Personal Computer, require the operator to make control selections at the keyboard, perhaps selecting the mode of operation or particular image to be displayed, prior to using the interactive input device for inputting data to the system. For example, in hotel management applications, the operator would enter control information at the keyboard to select either a first displayed image for a room assignment application or a second displayed image for entering billing information. Only after having made the control input at the keyboard, will the operator be able to make data entries by means of the interactive input at the display surface.